Technical Field
The present invention relates to a braking control method and system for an eco-friendly vehicle. More particularly, it relates to a braking control method, a braking control system, and a non-transitory computer readable medium for an eco-friendly vehicle, which can solve a problem of deterioration of braking reliability due to influence of environmental conditions in performance of vehicle braking through distribution of regenerative braking and friction braking, in order to satisfy a driver request braking amount.
Description of the Related Art
Conventional internal-combustion engine vehicles using fossil fuel such as gasoline or diesel have several problems including environmental pollution due to exhaust gas, global warming due to carbon dioxide, occurrence of respiratory diseases due to generation of ozone, and the like.
Accordingly, there have been developed eco-friendly vehicles, such as an electric vehicle (EV) driven by electric power, i.e., utilizing an electric motor, a hybrid electric vehicle (HEV) driven by an internal-combustion engine and an electric motor, and a fuel cell electric vehicle (FCEV) driven by driving an electric motor using electric power generated from a fuel cell.
In an eco-friendly vehicle, a regenerative mode is performed in which braking or inertia energy in braking of the vehicle or coasting by inertia is collected through generation of electric power using an electric motor and then charged in a battery (motor charge).
As such, in the braking or coasting of the eco-friendly vehicle, energy is collected using the electric motor, and the battery is charged with the collected energy. Thus, the energy can be efficiently used, and the fuel efficiency of the vehicle can be improved.
Particularly, a regenerative braking system of the eco-friendly vehicle converts kinetic energy of the vehicle into electric energy in braking of the vehicle, and stores the converted energy in the battery. Then, the regenerative braking system enables the stored energy to be reused in driving the electric motor, thereby improving the fuel efficiency of the vehicle.
Such a regenerative braking technology is a core technology of an eco-friendly vehicle, in which, in order to maximize fuel efficiency, electric energy is generated by applying a reverse torque to an electric motor using energy generated during braking, and the generated electric energy is stored in a battery, thereby enabling reuse of the stored electric energy in driving of the vehicle. The regenerative braking technology is applied to most eco-friendly vehicles.
Meanwhile, a vehicle controller (hybrid control unit (HCU)/vehicle control unit (VCU)), as an uppermost-level controller for controlling all operations of the eco-friendly vehicle, is mounted in the vehicle. In addition, the eco-friendly vehicle is provided with a variety of controllers for controlling various devices of the vehicle.
For example, the eco-friendly vehicle is provided with a brake controller for controlling the operation of a friction brake (friction braking device), a motor controller (motor control unit (MCU)) for controlling the operation of a motor, a transmission controller (transmission control unit (TCU)) for controlling the operation of a transmission, a battery controller (battery management system (BMS)) for collecting information on states of a battery to use the collected information in battery charging/discharging control or to provide the collected information to the other controllers, and the like.
The vehicle controller and each controller perform cooperation control while communicating information with each other through controller area network (CAN) communication. In this state, an upper-level controller transmits control commands to the lower-level controllers while receiving and collecting various information transmitted from the lower-level controllers.
Main functions of controllers related to regenerative braking in an eco-friendly vehicle will be briefly described with reference to FIG. 1 (RELATED ART). The regenerative braking is basically performed through cooperation control of a brake controller 10 for performing friction braking (hydraulic braking), a vehicle controller 20 for determining a regenerative braking execution amount and a regenerative braking motor torque command, a motor controller 30 for performing regenerative braking by controlling the torque of a motor according to the motor torque command, a battery controller (not shown) for providing information on a state of a battery, and a transmission controller (not shown) for providing information on a state of a transmission.
The brake controller 10 determines a request braking amount according to a driver's brake pedal input, i.e., a total braking amount. The brake controller 10 determines a regenerative braking permissible amount through distribution of braking power and transmits the determined regenerative braking permissible amount to the vehicle controller 20.
Accordingly, the vehicle controller 20 determines a motor torque command according to the regenerative braking permissible amount, and transmits the determined motor torque command to the motor controller 30.
Also, the vehicle controller 20 determines a regenerative braking execution amount in consideration of states of the motor and the transmission, and transmits the determined regenerative braking execution amount to the brake controller 10.
The motor controller 30 controls the torque of the motor through an inverter according to the motor torque command (regenerative braking command) received from the vehicle controller 20, and transmits information on a motor output torque, etc. so that the vehicle controller 20 can estimate the regenerative braking execution amount.
The brake controller 10 controls friction braking satisfying the total braking amount with reference to the regenerative braking execution amount received from the vehicle controller 20.
In particular, the brake controller 10 determines a friction braking amount (hydraulic braking amount) obtained by subtracting the regenerative braking execution amount from the total braking amount, and then controls the operation of a friction braking device (hydraulic braking device) to generate braking power corresponding to the friction braking amount (performance of friction braking).
The transmission controller performs control on a vehicle transmission such as an automatic transmission (AT) or a dual clutch transmission (DCT), and transmits information on a transmission state (transmission gear ratio), etc. to the vehicle controller 20 so that the vehicle controller 20 can determine the regenerative braking execution amount.
As such, in the conventional eco-friendly vehicle, the brake controller 10 calculates a regenerative braking permissible amount, the vehicle controller 20 calculates a motor torque command according to the regenerative braking permissible amount, and the motor controller 30 controls the motor according to the motor torque command (performance of regenerative braking).
The vehicle controller 20 calculates a regenerative braking execution amount using information on states of the motor and the transmission and then transmits the calculated regenerative braking execution amount to the brake controller 10. The brake controller 10 performs distribution of braking power using the regenerative braking execution amount and then controls the friction braking device to generate the distributed friction braking power (performance of friction braking).
FIGS. 2 and 3 (RELATED ART) are flowcharts illustrating in detail a braking control process of an eco-friendly vehicle. If a driver manipulates the brake pedal 1, the brake controller 10 determines a total braking amount (S11) according to a pedal stroke (pedal manipulation depth) sensed by a sensor (brake pedal stroke sensor: BPS) (S11), and determines a regenerative braking permissible amount through distribution of braking power (S12 and S13).
The regenerative braking permissible amount is transmitted to the vehicle controller 20. The vehicle controller 20 determines a regenerative braking possible amount according to vehicle conditions (S14) and then determines a regenerative braking torque from the regenerative braking possible amount, using information on the maximum charging power as information on a state of the battery, received in the battery controller 40, and information on the maximum charging torque as information on a state of the motor, received in the motor controller 30 (S15). The vehicle controller 20 determines a motor torque command from the regenerative braking torque (S16) and transmits the determined motor torque command to the motor controller 30.
Accordingly, the motor controller 30 controls the torque of the motor through the inverter according to the motor torque command received from the vehicle controller 20 (S17), thereby performing regenerative braking (S18).
In addition to the performance of the regenerative braking, friction braking is controlled by the brake controller 10. First, the vehicle controller 20 calculates a regenerative braking execution amount according to a change of speed, using information on a state of the transmission, received in the transmission controller 50, from the regenerative braking torque (S19, S20 and S21).
If the regenerative braking execution amount is determined (S23), the vehicle controller 20 transmits the regenerative braking execution amount to the brake controller 10. The brake controller 10 receives the regenerative braking execution amount from the vehicle controller 20 (S24), and determines a friction braking amount obtained by subtracting the regenerative braking execution amount from the total braking amount (S25).
As a result, the brake controller 10 controls the friction braking device to generate braking power corresponding to the friction braking amount, thereby performing friction braking (S26).
However, the braking control process described above has problems as follows.
In the case of the friction braking (hydraulic braking), braking power is directly applied to vehicle wheels using friction. Hence, a difference in braking power is generated according to an environment.
However, in the case of the regenerative braking, braking power is generated using the motor, and hence the regenerative braking is hardly influenced by the environment. Therefore, when the environment is changed, it is impossible to control the addition of braking powers (impossible to satisfy the total braking amount), and the reduction of speed in the vehicle is considerably changed depending on a ratio of the regenerative braking amount not influenced by the environment and the friction braking amount relatively considerably influenced by the environment.
FIGS. 4 and 5 (RELATED ART) are views illustrating problems according to the conventional art. FIG. 4 shows an example of normal regenerative braking cooperation control slightly influenced by an external environment. FIG. 5 shows an example of abnormal regenerative braking cooperation control considerably influenced by the external environment.
As shown in FIG. 4, when the environmental fluctuation amount is not more than a predetermined level, the reliability of friction braking (hydraulic braking) is high, and a total braking command value is equal to an actually performed total braking execution amount. Thus, the braking linearity is high (total braking command value=regenerative braking execution amount+friction braking execution amount=total braking execution amount).
On the other hand, as shown in FIG. 5, when the environmental fluctuation amount is not less than the predetermined level or higher, the reliability of friction braking (hydraulic braking) is relatively low, and the total braking command value is not equal to the actually performed total braking execution amount. Therefore, it is difficult to ensure the braking linearity (total braking command value≠regenerative braking execution amount+friction braking execution amount=total braking execution amount).
As a result, a difference in actual braking deceleration of the vehicle is considerably generated according to external environmental conditions even under the condition of the same driver brake pedal manipulation depth (brake depth).